1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, relates to a liquid crystal display device and a method of fabricating the same.
2. Discussion of the Related Art
Many types of flat panel displays have been developed to serve as substitutes for cathode-ray tubes (CRTs), such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays, and electro-luminescence displays (ELDs). LCD devices have many advantages over CRTs, including higher resolution, thinner profile, more compact size, and lower power usage during operation.
LCD devices generally include two substrates that are spaced apart and face each other and a liquid crystal layer interposed between the two substrates. The two substrates also include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal layer. Alignment of the liquid crystal molecules in the liquid crystal layer changes in relation to the intensity of the induced electric field which alters the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field within respective pixel regions that are provided with the LCD device.
LCD devices may be categorized into transmissive type, reflective type, and transflective type. Transmissive type LCDs require a backlight and consumes a relatively large amount of power during operation. Reflective type LCDs are operated with the aid of external light, and the brightness of the display is proportional to the amount of external light available. Transflective type LCDs are selectively operated in either transmissive or reflective modes. Transflective type LCD devices improve upon the disadvantages of the transmissive type and reflective type LCD devices.
Referring to FIG. 1, in an array substrate 1, a gate electrode 6, and a gate line (not shown) are formed on a first substrate 2. A gate insulating layer 10 is formed on the gate electrode 6. A semiconductor layer that is formed from an active layer 13 and an ohmic contact layer 16 is provided on the gate insulating layer 10 over the gate electrode 6. Source and drain electrodes 23, 26 are formed on the ohmic contact layer 16. Each of the gate electrode 6, the semiconductor layer, and the source and drain electrodes 23, 26 combine to form a thin film transistor Tr. A data line 20 is provided on the gate insulating layer 10. The data line 20 crosses the gate line to define a pixel region P. A first passivation layer 30 is formed on the data line 20 and the source and drain electrodes 23, 26. A reflective electrode 40 is formed on the first passivation layer 30 in a reflective region RA. A second passivation layer 45 is formed on the reflective electrode 40. A pixel electrode 50 is formed on the second passivation layer 45 in the pixel region P. The pixel electrode 50 contacts the drain electrode 26 through a drain contact hole 55.
In a color filter substrate 70, a black matrix 75 is formed on a second substrate 71. Red (R), green (G) and blue (B) color filters 80a, 80b, and 80c are formed in the corresponding pixel regions P. An overcoat layer 85 is formed on the color filters 80a, 80b and 80c. A common electrode 90 is formed on the overcoat layer 85.
A liquid crystal layer 60 is provided between the array substrate 1 and the color filter substrate 70. When voltages are applied to both the pixel and common electrodes 50, 90, an electric field is induced within the liquid layer 60, and the liquid crystal molecules therein are reoriented in proportion to the electric field. Although not shown in the drawings, an alignment layer is formed on each of the transparent and common electrodes 50, 90. Additionally, first and second retardation films 97, 95 may be formed on outer surfaces of the first and second substrates 2 and 71.
As best shown in FIG. 1, a cell gap d1 (i.e. the thickness of the liquid crystal layer 60) of the reflective region RA is substantially the same as a cell gap d2 of the transmissive region TA. In a reflective mode, an external light passes through the liquid crystal layer 60, then reflects on the reflective electrode 40, and then passes through the liquid crystal layer 60 again. Light in the reflective mode substantially travels as far through liquid crystal layer 60 as in the transmissive mode. Accordingly, there is a phase difference of light between the reflective and the transmissive modes.
To minimize or eliminate the phase difference, the transflective type LCD device of FIG. 2 provided. In the transflective type LCD device, a cell gap d4 (i.e. the thickness of the liquid crystal layer 60) within the transmissive region TA is substantially twice the cell gap d3 within the reflective region RA. Accordingly, the phase difference of FIG. 1 is substantially prevented because light travels through the same thickness of liquid crystal in both modes.
However, the transflective type LCD devices of FIGS. 1 and 2 have some problems. Light in the reflective mode passes through the color filter twice, and light in the transmissive mode passes through the color filter only once. Accordingly, color property differences between the reflective mode and the transmissive mode may occur. Also, the brightness in the reflective mode may be less than in the transmissive mode. Further, the reflectivity is reduced because the reflective electrode is flat.
Referring to FIG. 3, a through hole TH is formed in the color filters 80a, 80b and 80c in the reflective region RA. Light passing through the through hole TH in the reflective mode has substantially the same properties as light passing through the device in the transmissive mode, and brightness in the reflective mode is increased. Further, a first passivation layer 30 formed from two sub layers 30a, 30b has an uneven surface, which provides the reflective electrode 40 with a similar uneven surface. The uneven surface of the reflective electrode 40 increases the overall reflectivity. However, at least two mask processes are required to form the uneven surface. The additional mast process increase the fabrication time and product cost of an LCD device. Also, the processes of forming the uneven surface, makes it difficult to form a dual cell gap structure within the LCD panel.